Neuronal Control of Drosophila Walking Direction

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Science  04 Apr 2014:
Vol. 344, Issue 6179, pp. 97-101
DOI: 10.1126/science.1249964

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Backward or Forward

Although land animals generally walk forward, they readily switch to walking backward if they sense an obstruction or danger in the path ahead. Such a switch is likely to involve a neural signal sent from the brain down to local motor circuits, instructing these motor circuits to alter the phase at which specific leg muscles are activated. Bidaye et al. (p. 97; see the Perspective by Mann) identified such a neuron in Drosophila, which they call MDN (moonwalker descending neuron). Blocking synaptic transmission from MDN inhibited backward walking, and conversely artificially activating MDN caused flies to walk backward.


Most land animals normally walk forward but switch to backward walking upon sensing an obstacle or danger in the path ahead. A change in walking direction is likely to be triggered by descending “command” neurons from the brain that act upon local motor circuits to alter the timing of leg muscle activation. Here we identify descending neurons for backward walking in Drosophila—the MDN neurons. MDN activity is required for flies to walk backward when they encounter an impassable barrier and is sufficient to trigger backward walking under conditions in which flies would otherwise walk forward. We also identify ascending neurons, MAN, that promote persistent backward walking, possibly by inhibiting forward walking. These findings provide an initial glimpse into the circuits and logic that control walking direction in Drosophila.

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